The invention refers to a coating system for the decorative layering of work pieces, which can be galvanized.
Coating systems of this type are known from the current state of the art, and they are applied especially in the automotive and the furniture manufacturing industry, as well as in the sanitary equipment area. The possible variety of galvano-decorative coatings is in an upward trend, involving the coating of not only basic materials consisting of iron or zinc but also a variety of basic materials such as plastics, for example. Of special interest in this connection are the typically possible metallic matte and bright effects. In order to protect against discoloration and corrosion, these matte and bright effect generating layers are generally covered with a chromium layer, which usually has a blue-silver appearance and therefore fills numerous decorative requirements. For the protection of a metallic base material, coating systems are preferred which contain copper, nickel and chrome or nickel and chrome. Provided that the metals forming the protective coat are more noble than the base material, such a system provides corrosion protection since corrosion only occurs if the protective coat has irregularities such as pores or grooves, for example, which extend to the base material. This limited corrosion resistance of the currently known coating systems, however, increasingly no longer can meet the stringent requirements of the automotive industry.
In addition to an improvement of resistance to corrosion, the use of a decorative coating has the aim to create an improved over-all appearance. With respect to coloration, the blue-silver appearing chrome cover coat can be replaced by tin, silver, gold, palladium or rhodium, for example. However, the disadvantage is that with this type of substitute cover coats neither good corrosion protection nor a high degree of wear resistance can be achieved.
In order to improve the wear resistance it is known from the current state of the art to form a mechanically resistant material coat by means of a vacuum coating process, using mechanically resistant material particles such as titanium or zirconium compounds, for example, and thus creating a cover coat with a higher degree of wear resistance. Here, two different basic vacuum coating processes exist for the deposition of mechanically resistant material coatings: CVD (chemical vapor deposition) and PVD (physical vapor deposition). Both processes, however, share the disadvantage of the mechanically resistant material coats in the customary coat thickness range being too porous, and therefore they cannot contribute anything to the corrosion protection of the over-all coating system. As a result, even a coating system, which has a mechanically resistant material coat as the cover coat, does not meet the corrosion resistance requirements.